Automatic telephone system



March 1o, 1925. 1,528,792'

R. G. RICHARDSON AUTOMATIC TELEPHONE SYSTEM Original Filed'Feb. 13, 1920Bourne Eznhar'afsan.

Patented Mar. 10, 1925.

UNITED STATES 1,528,792 PATENT OFFICE.

RODNEY G. RICHARDSON, F CHICAGO, ILLINOIS, ASSIGNOCR. T0 AUTOMATICELECTRIC COMPANY, 0F CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS..

AUTOMATIC TELEPHONE SYSTEM.

Application led'February 13, 1920, Serial No. 358,382. -Renewed July 23,1924.

To all whom it may concern Be it known that I, RQDNEY G. RICHARD- SON, acitizen of the United States of America, and resident of Chica o, in thecounty of Cook, in the State of llinois, have invented certain new anduseful Improvements in Automatic Telephone Systems, of

which the following is a specification.

My invention relates in 0'eneral to automatic telephone systems and hasfor its object. the provision of a large capacity automatic telephonesystem without increasing the number of digits in the subscriberstelephone numbers.

The general type of automatic system in common use is what is known asthe Strowger percentage trunking system. It is strictly a decimal systemand'employs ver- -tical and rotary selector vand connector switcheshaving ten levels of bank contacts and ten contacts per level. Thecapacity of a system of this kind depends on the number of selectorswitches used in a complete connection. Each group of connectors has acapacity of 100 lines and if first selectors only are employed therewould be ten groups of connectors, giving a capacity of 1000 lines. If alarger system is desired, so called second selectors are introducedbetween the first selectors and thc connectors, increasing the size to10,000 lines. Still larger systems may be had by adding third selectors,or fourth selectors, giving ultimate capacities of 100,000 and 1,000,000lines, respectively. Thus the capacityrmay be increased to any desiredextent.

But as soon as the size gets beyond 10,000

lines certain difficulties present-themselves. One of the principalobjections is the diiiiculty experienced by the subscribers inremembering the digits in the 'telephone numbers. A system of 10,000lines has 4 digits, a 100,000 line system has 5 digits, and a 1,000,000line system has 6 digits, in each telephone number. It has been found byexperience that 4 digits is all that a subscriber can rememberconveniently from the time helooks the number up in the directory untilhe has completed calling it on his dial. Obviously also the liability ofactual error on the part of the. subscriber is increased in proportionto the number of operations he has to perform, regardless of whether hismemory is faulty or'not; and this applies also to the operation of theswitches, for the possibility of switch failure is proportional to thenumber of switches required to be operated. These considerations showdiiiiculties which are in addition to the others naturally consequent onthe use of an unduly large number of selector switches in serialrelation, which results in an excessively eX panded trunking system withall the attendant complications.

Numerous eilorts have been made in the past to provide a large capacitysystem without unduly increasing the digits in the telephone numbers,and therefore the trunking operations required to set up a connection,but without entire success, so far as I am aware. One of the mostobvious things to do, and one which has been availed of before, althoughin a different way, is to increasel the size and capacity of theswitches; and this is the way in which I have approached the problem. Iprovide switches which have 20, 30, or 40 levels, as the case may be,instead of only 10 levels. The connectors will of course have the samenumber of Contact sets in each level as there are levels, while this mayor may not be true of the selectors, depending on the desired size ofthe trunk groups.

In order to operate these large size switches I provide what I term amultiple impulse calling device. In this calling device the number ofrows of finger holes, ten holes per row,- is equal to the number oflevels in one of the central oflice switches divided by ten. Thus in alevel system the calling devices will have two rows of finger holes,while in a level system the calling devices will have three rows ofiinger holes, etc. In the operation of the calling device the impulsestransmitted are not equal to the numerical designation of the fingerhole used to operate it, but are equal to a multiple of such numericaldesignation. Thus in a 20 level system if the digit 1 is called, twoimpulses will be transmitted, if the digit 5 is called 10 impulses,while a maximum of 20 impulses results from the calling of the digit 0.In the same way, in a 30 level system, if the digit 5 is called 15impulses will be transmitted, and a maximum of 30 impulses will betransmitted if the digit 0 is called. The multiple impulse principle isapplied to all the rows of finger holes on the calling device the sameway except that in the case of every row except ltended to idle firstselector switches.

, mitted will be one less than in the previous case. In a 3() levelsystem, in which the calling devices have three rows of finger" holes,if a digit is called on the inner row of finger holes, for example, thedigit 5, exactly three times as many impulses or 15 impulses will beproduced; if the corresponding finger hole in the next row is used onelimpulse is omitted from the beginning of the series and 14 impulses areproduced; and

if the corresponding finger hole in the outside row is used two impulsesare omitted and 13 impulses are produced.

It will be seen that the purpose of omitting one or more impulses is toenable the switches to Operate on those levels which are not exactmultiples of the digits 1 toO,

inclusive, thereby permitting all the levels to be used. Separatedesignations are used to indicate correspondino nger holes in theseveral rows, so that t e subscribers will -know by the telephonenumbers which row to use in the case of each digit or element of thenumber. This however is a detail which will be explained later inconnect-ion. with the more detailed description of the appara# tusemployed in which reference will be made to the accompanying drawings.

The specific embodiment of the invention with which I-` have chosen toillustrate the same in the present application is a 2() level system.Fig. 1 shows a schematic diagram of the trunking, with the numbering ofthe bank levels; Fig. 2 is a view of ak calling device adapted for usein the system shown invFig. 1; Fig. 3 shows a type of impulse cam whichmay be used in the calling device; while Fig. 4 is a skeleton diagram ofthe control circuit for a series of the central office switches,

Referring to Fig. 1 I will first explain the trunking scheme briefly.Three subscribers telephone stationsare indicated by the circles at theupper left hand corner of the diagram. These stations are connected bythe usual line circuits with the exchange, where they terminatepreferably in line switches of some kind through the medium of which thelines when calling may be eX- The first selectors are the first in theseries of numerical switches'which are used to estab- )ish connection inaccordance with called telephone numbers. The three squares labeledFirst selectors indicate three of these switches, and the multiple banksthereof, comprising 2O levels of contact sects are indicated by the 20heavy horizontal lines. From each first selector level trunk linesextend to a group of second selectors, there being in all 20 groups ofsuch second selectors. The group in which the trunk lines from the firstselectornlevel terminate is indicated in the drawing by three moresquares, labeled Second selectors, and the multipie banks are indicatedby 20 horizontal lines as in the case of the first selectors. Each groupof \second selectors has access through its Q0 bank levels to 2O groupsof connectors. As in the case of the second selectors, only one group ofconnectors is shown, this being the group accessible from the firstlevel of the group of second selectors shown. The connectors arelikewise indicated by three squares, which are labeled Connectors in thedrawing, and the banks are indicated by the heavy lines as before. Itwill be seen that the trunking scheme as a whole is similar to the usualone in common use, the only substantial difference being in the capacityof the switches.

In mechanical construction the selector and connector switches may be ofthe ordinary vertical and rotary type, as shown in the U. S. Patents toKeith, Erickson, and Erickson, Numbers 815,321 and 815,176, the verticalshafts, however, being provided with more notches corresponding to theincreased number of bank levels. The circuits vmay be of the well knowntwo-wire. type, as illustrated by the U. S. Patent to Newforth, No.13,901, reissued April 13, 1915, as much of the circuits as is necessaryfor an understanding ofthe method of switch control being shown in Fig.4.

The. numbering of the bank levels will now be considered. As shown inthe drawing, lthe evenlevels,` second, fourth, sixth, etc., correspondto the digits 1, 2, 3, etc., which are the designations appearingbeneath the finger holes of the inner row of finger holes on the callingdevices; while the odd levels, first, third, fifth, etc., correspond tothe letters A, B, F, etc., which are the designations appearing beneaththe finger holes of the-outside row on the calling devices. In -theconnectors, the. individual contact sets in each level are similarlynumbered, for they are selected by numerical operations under controlofthe calling devices.

Inasmuch as the connectors have 20 levels and 20 contact sets in eachlevel, the capacity of each group of connectors will be 400 lines. Thereare 2O groups of connectors accessible to each group of secondselectors, which would give each group of second selectora access #08000lines; and since there are --20 groups rof second selectors the totalcapacity ofthe 2O level system shown will be 160,000 lines. When thisnumber of lines is com ared with the capacity of the kordinary our digitdecimal system, which is 10,000 lines, the enormous increase in capac-vA .I will now describe the calling device more in detail, for thepurpose of explaining the multiple impulse princi le and its applicationto the control o the central oflice switches. In general, the callingdevice Ashown is of the rtwo wire type as described on pages 34 and 35of Automatic Telephony, by Smith and Campbell. .An improved form of thiscalling device is shown and described in the U. S. ,Patent to Keith, No.1,27 9,352. There are certain changes, however, which will be pointedout. In the first place the number of impulses transmitted for any givendigit must be multiplied by 2. This can be accomplished by altering ,thegear ratio, and in thelarger systems using a multiplier of 3 or 4,changing the gear ratio is the preferred way. But in/the twenty levelsystem, the desired result may be accomplished very easily bysubstituting an impulse cam having four blades for the usual cam havingonlytwo. This is the means employed in the calling 4 device shown in thedrawing, the `four bladed impulse cam being shown in Fig. 3.

It will be clear from the above that when any digit is called exactlytwice as many interruptions will be produced by the 'impulse springs.For instance, if we assume that a first selector is being operated, asfor example, the first selector shown in Fig. 4, if the digit l iscalled, two interruptions will be produced and the selector wipers willbe raised to the second level, if the digit 2 is'W called, fourinterruptions will be produced and the wipers will be raised tothefourth level, and so on. This much being vunder- 4stood it'remains to`be seen how the proper number of interruptions is produced by callingthe letters A. B, E, etc., to raise the selector wipers to the oddlevels. In order to make this latter clear two radii are shown in dottedlines passing through the centres of the first two finger holes in eachrow.

Also -two other radii are shown which in.

dicate the angular limit of movement of the dial when operatedfrom'finger holes in the two rows, respectively. These radii pass throuh the centre of the dial and it will be seen t at the crown teeth on thelarge gear wheel (adapted to be engaged by a dog on the under surface of-.thediaD are spaced in definite relation thereto. Thus there areexactly two crown teeth in the angular distance between any two adjacentfinger holes. Now if the digitl is pulled on the dial the dog will bemoved past two crown teeth and upon the dial being released will engagethe second tooth and rotate the mechanism sufficient to produce twointerruptions. But if the letter A is pulled on the dial, owing to thedisplacement of the outside portion of the finger stop, whichdisplacement is exactly equal to the angular distance between adjacentcrown teeth, the forward movementof the dial will be stopped after thedog"has been moved past one of the crown teeth, and it follows that whenthe dial is released the mechanism is rotated only half as far, orsufficient to produce one interruption. If the letter B is pulled, thedog will of course be moved past two teeth while the dial is being movedthe angular distance` between inger holes B and A, just the same asthough the digit 2 had been called, but the further movement to thelimit fixed by the finger stop only results in moving the dog pastonemore tooth, and when the dial'is released a total of three interruptionsare produced. The operation of producing one or three interruptions willnaturally result in raising the selector either one or three steps, asthe case may be, and since these same considerations apply to thecalling of the refrom the foregoing. A larger dial must be used havingan additional row of finger holes, which may be numbered in accordancewith the last ten letters of the alphabet, the second row of holes being.numbered in accordance with the first ten. As before stated, the gearratio should also be changed to provide for producing threeinterruptions when the digit one is called. The angular distance betweenadjacent crown teeth on the gear wheel will be one third the angulardistance between adjacentfinger holes, and a three position finger stopwill be used in which the displacement between the first and secondpositions, and between the second and third positions, is equal to theangular distance between adjacent crown teeth. A calling device soconstructed vis adapted to operate a selector to raise its wipers to anyaoV es i

, to 400 lines.

desired level in a total of30 levels. By following the same generalprinciplesa calliiw device may be constructed for a 40 level system, ora still larger system, although it is believed that it will be foundimpracticable to use switches havingl more than 40 levels. f

It will be understood from the foregoing that the telephone numbers in asystem constructed in accordance with my invention may be composedsolely of digits, of letters, or of a mixture of the two. Thus in the 2Olevel system shown there will be certain numbers which are calledentirely on the inner row of finger holes, as #1234, for example. Thenthere will be numbers like A B F H, for example, which are calledentirely on the outside row of holes; and finally there are thecomposite numbers such as q A 2 F 4, which form the greater portionl ofthe total, and which are called in part on each row of holes. The mixingof figures and letters causes no confusion, but rather facilitates theremembering of a number, and since a system of the largest required sizecan be built according to these principles to use a maximum of fourdigits or other elements, the great advantages of the invention will beevident.

There are other advantages not hitherto mentioned, the principal one ofwhich is the great economy in switches which results from the largecapacity of the switches and the large size of the trunk groups. Forexample, each group of connectors has access About 25 or 30 connectorswould be sufficient under ordinary conditions to handle the trafiic,while if the 400 lines were divided into four 100 line groups each suchgroup would require ten connectors, or a total of forty. But theincreased efficiency which results from large groups is Vwell understoodand need not be further commented upon.

While I have shown and explained a certain specific form of my inventionwith certain modifications thereof, I am of the opinion that othermodifications can be made which may be of advantage under certaincircumstances, without departing beyond the real scope of the invention,and I do not therefore wish to limit the invention to the exact formsdescribed, but desire to include and have protected by Letters Patentall forms thereof which come within the scope of the appended claims:

What I claim as my invention is:

l. In a telephone system, an automatic switch, a plurality of groups oflines accessible to said switch, a calling device for controlling saidswitch by current impulses, a movable dial for said device, a series ofadjacent finger holds on said dial less in number than the number ofsaid groups, and multiplying impulse sending mechanism controlled bysaid dial and capable of sending a maximum number of impulses equal tothe number ofsaid groups.

2. In a telephone system, a calling device, a movable dlal having aseries of finger holds for use in operating said device in accordancewith the digits in called telephone numbers, an automatic switch, and

mechanism controlled by said dial each time it is operated for producingcurrent impulses to=operate said switch, the number of impulses producedeach time being a whole multiple of the digit called.

3. In a telephone system, an automatic switch, trunk lines accessible tosaid switch divided into main groups and sub-groups, a calling devicefor controlling said switch having separate series of operating meanscorresponding in number to said groups and sub-groups, and impulsesending mechanism controllable by any of said operating means, andadaptedto produce a maximum number of impulses equal'to the total numberof said sub-groups.y

4. In a telephone system, an automatic switch, trunk lines accessible tosaid switch divided into main groups and sub-groups,

ger holkds being equal to the total number of said sub-groups, andimpulse sending mechanism controlled byl said dial when the same isoperated, and arranged to produce a maximum number of impulses equal tothe total number of said sub-groups.

5. In a telephone system, an automatic switch, a calling device forcontrolling said switch, a movablememb'er forming part of said devicehaving two series of finger holds, and impulse sending mechanismcontrollable by said member to produce an even number of impulses whenthe member is operated from any finger hold in one series, and an oddnumber of impulses when the member is operated from any finger holdinthe other series.

6. In a telephone system, a calling device having a movable dial, twoseries of finger holds on said dial, impulse sending mechanismcontrollable by said dial to produce an even number of impulses when thedial is operated from any finger hold in one series,

and an odd number of impulses when the switch, twenty groups of linesaccessible to said switch, a calling device for operating .said switchby curi-ent impulses, a dial for said device having. two rows of fingerholds.y there being ten finger holds in each row, an impulse sendingmechanism. controllable by said dial to transmit current impulses tosaid switch, the number of impulses being equal 'to twice the number ofthe finger hold in thevrow when the dial is operated from a finger holdin one of said rows, and being equal to twice the number of the fingerhold in the row less one when the dial is operated from a finger hold inthe other of' said rows.

8. In a telephone system, an automatic switch, roups of lines accessibleto said switch tige number of said groups being a multiple of ten, acalling device for operating said switch by current impulses, a dial forsaid calling device having a plurality of rows of finger holds, therebein ten finger holds in each row, an impu se sending mechanismcontrollable by said dial when the same is operated from a finger holdin one of said rows to transmit current impulses to` said switch whichare equal in number to a multiple of the number of the finger hold inthe row, and which are equal in number to a multiple of the number ofthe finger hold in the row less one or more impulses when the dial isoperated from any other finger hold. y

9. In a telephone system, a calling device, a. movable dial having twoseries of finger holes for operating said device, one series of holesbein marked in accordance with' the digits in t e telephone numbers,while the other series of holes is marked in accordance with otherlcharacters also forming partof the telephone numbers, an automaticswitch, and mechanism controlled by said dial each time itis operated toproduce current impulses to operate said switch, the number of impulsesproduced when the dial is operated 1n accordance with any digit being amultiple of the digit called, and the number of impulses produced whenthe dial isoperated in accordance with one of said other charactersbeing equal to a multiple of the corresponding digit less one.

10. Ina telephone system, a calling device, a movable dial having twoseries of finger holes for operatin said device, one series of holesbeing, marIred` in accordance with the digits in the telephone numbers,while the other series of holes is marked in accordance with 'othercharacters 4also forming part of the telephone numbers, an automaticswitch, mechanism controlled by said dial each time it is operated toroduce current impulses to operate said switch, the number of impulsesproduced when the dial is operated in accordance with an. digit being amultiple of the di it called, and means for causing one impu sc to beomitted when the dial is operated in accordance with one of said othercharacters,'whereby the number of impulses roduced will ble equal toA amultiple of t e corresponding digit less one.`

11. In a telephone system, a calling device, a movable dialhavin twoseries of finger holes for operating said device, one series of holesbeing marked in accordance with the digits in the telephone numbers,while the other series of holes is marked in accordance with othercharacters also forming part of the telephone numbers, an automaticswitch, mechanism controlled by said dial each time it is operated toproduce current impulses to operate said switch, the number of impulsesproduced when the dial is operated in accordance with any digit being amultiple of thev digit called, and a two position finger sto oneposition of said stop being displace a definite amount so as to causeone impulse to be omitted when the dial is operated in accordance withone of said other characters, whereby the number of impulses produced isequal to` a multiple of the corresponding digit less one.

12. In a calling device for automatic telephone system, a rotatable dialhaving a row of finger holds marked in accordance with the ten digits,and mechanism controllable by said dial to produce current impulses, thenumber of impulses produced being a whole multiple of the digit called.

13. In a telephone system, automatic switches having bank contactsarranged in different groups. the number of groups being a multiple often, calling devices having each a plurality of operating means arrangedin separate rows, the total number of said operating means being equalto the number of said groups and the number of said rows being equal tothe number of said groups divided by ten. multiplying impulse;

sending mechanism for sending impulses in accordance with a multiplierwhich is equal to the total number of said-rows, and means for omittingimpulses when said device is actuated by operating means in certain ofsaid rows, the number of impulses omitted being equal to the number ofthe row used minus one.

14. In a calling device for automatic telephone systems, a rotatabledial having two concentric rows of finger holds, a two position fingerstop, one position being displaced from the other an angular distanceequal to one half the angular distance between any two adjacent fingerholds, and impulse transiitlting mechanism controlled by the said 15. Ina calling device for automatic telephone systems, impulse sendingmechanism, a rotatable dial for controlling said mechanisni, said dialhaving a luralit of concentric rows of finger hollds, an a finger stopfor limiting the rotation lof the dial,Y

said finger stop having a corresponding plurality of limiting positionsangularly displn ced from one another, whereby the rotary movement ofthe dial may be stopped at diii'erent points depending on the row offinger holds from which it is operated.

16'. In a calling device for automatic telephone systems, impulsesending mechanism, a rotatable dial for controlling said mechanism. aplurality of concentric rows of finger holds for rotating said dial, andmeans for stopping the rotation of said dial at different pointsdepending on the row of finger holds from which it is operated.

17. In a calling device for automatic tele? phone systems, impulsesending mechanism,

a rotatable dial for controlling said mecha-4 nism, a pluralityy ofconcentric rows of finger holes for rotatmg said dlal. the correspondingholes 1n each row being located on the same radii, and means forstopping the rotation of said dial at different points depending on therow of finger holes from` which it is operated.

182 In a telephone system, an` automatic.

19. In a telephone system, an 'automatic swltch, trunk lines accessibleto sald switch divided into main groups' and sub groups,

a calling device for controlling said switch, a movable dial for saiddevice havin series being equal to the number Io said SSP? .1 arateseries of finger holes, the num er of p main groups, corresponding nerholes in produceA a maximum number of impulses,

equal to the total number of said sub groups. N t

20. In a telephone system, an automatic `switch, groups of linesaccessible to said switch, a number of said groups being in multiple often, a calling device for operating said switch by current impulses, adial for said calling device having a plurality of rows of ringer holes,there being ten finger holes in each row with corresponding finger holeson the same radii, an im ulse sending mechanism controllable by saiddial when the same is operated` from a inger hole in one of said rows totransmit current impulses through said switch which are equal in numberto a multiple of the digit sent, and which are equal in number to amultiple of the digit sent less one or more impulses when the dial isoperated from` any other finger hole.

ASigned by me at Chicago, Cook County, Illinois, this 7th day ofFebruary, 1920.

RODNEY G. RICHARDSON.

